The field of automated biometrics is concerned with establishing or authenticating the identity of a subject (in general a human being) based upon characteristics that are in the possession of the subject. This process can be performed remotely over a network. A whole spectrum of biometric identification and authentication characteristics are biologically associated with human beings (and other animate objects), and, depending on the expressive power of the characteristic, more or less uniquely distinguish a subject from other subjects. A set of these types of characteristics are based on the skin pattern and/or the form of body parts. Examples of these biometric identifiers are: fingerprints, palm prints, hand prints; while more esoteric ones are: toe prints, ear prints, tongue prints, et cetera. The means of acquiring these types of characteristics is through a form of contact sensing. This contact sensing inherently effects the biometric characteristic and may in fact distort and corrupt the characteristic.
There exist systems that accomplish automatic verification or identification of a person (subject) using his/her fingerprint. A fingerprint of a person comprises a distinctive and unique ridge pattern structure. For identification/verification purposes, ridge pattern structure could be characterized by endings and bifurcations of the individual ridges. These features are popularly known as minutiae.
An example of part of a fingerprint is shown in FIG. 1A. The minutiae for the fingerprint shown in FIG. 1A are shown in FIG. 1B as being enclosed by "boxes." For example, box 101B (in FIG. 1B) indicates a bifurcation minutia of a bifurcated ridge 101A in FIG. 1A while box 103B indicates a ridge ending minutia of ridge 103A in FIG. 1A. Note that minutiae on the ridges in fingerprints have directions (also called orientations) 105 (FIG. 1B) associated with them. The direction of the minutia at a ridge ending 103B is the direction 113B in which the end of the ridge points. The direction of a bifurcation minutia 101B, on the other hand, is the direction 111B in which the bifurcated ridge points. Minutiae also have locations which are the positions of the minutiae on the fingerprint with respect to some coordinate system (not shown).
The prevalent fingerprint identification and verification methods are based on these minutiae features. Identification/authentication systems that use minutiae features need to process the fingerprint images to obtain accurate and reliable minutiae features to effectively determine or verify the identity of a person.
FIG. 2 is a flow chart showing the steps generally performed by a typical prior art system 200. In step 210, the image is acquired. This acquisition of the image could either be through a CCD camera and framegrabber interface or through a document scanner communicating with the primary computing equipment. Typically, the image is acquired through some means of contact sensing. Once the image is acquired into the computer memory or onto disk, relevant features minutia features are extracted (220). Not all of the features thus extracted are reliable. Some of the unreliable features are optionally pruned (step 230), e.g., manually edited. The resultant reliable features are used for matching two fingerprint images (step 240), that is, matching the acquired fingerprint image with stored minutiae representations of previously acquired fingerprint images.
The following reference further describes examples of the state of the prior art:
N. K. Ratha, S. Chen, and A. K. Jain, PA1 Adaptive flow orientation based texture extraction in fingerprint images, PA1 Pattern Recognition, vol. 28, no. 11, pp. 1657-1672, November 1995. PA1 1. Method for optical comparison of skin friction-ridge patterns, to W. White, U.S. Pat. No. 3,200,701, issued Jan. 29, 1962. PA1 2. Fingerprint Identification System Using a Pliable Optical Prism, to V. A. DePalma and R. W. King, U.S. Pat. No. 4,120,585, issued October 1978. PA1 3. Portable Fingerprint Scanning Apparatus for Identification Verification, to G. M. Fishbine et al., U.S. Pat. No. 5,467,403, issued November 1995.
This reference is incorporated herein by reference in its entirety.
It is often desirable to use inkless methods of acquiring fingerprint images. Such systems require the fingerprint to be placed on a prism surface and, using the frustrated internal reflection method, the image is captured by a video camera. U.S. Pat. No. 5,467,403, for example, to Fishbine et al. discloses the means and methods for live-scan fingerprint image acquisition. This method of image acquisition is also known as the live-scan method.